Portions of this invention are very closely related to earlier coowned patent documents directed to optical systems and methods for imaging, and for noticing and optically following a large variety of objects outside an optical system. These innovations included capabilities for “steering” of radiation beams, using any of a great variety of optical-deflection or -switching arrangements.
Such arrangements comprised using pointable mirrors of many different types, and other kinds of routing devices such as an optical-switch “fabric”, and birefringent and other nonlinear materials, all generally positioned within an optical system. The mirrors included individual reflectors, and reflector arrays, over a broad range of sizes and typically controllable in two axes of rotation as well as in some cases piston movement.
Some of the mirrors were microelectromechanical system (“MEMS”) units or other micromechanical devices—i.e. not limited to electrical or electronic control. Among the relatively larger mirrors (for instance those over 5 mm across) were magnetically driven individually steering mirrors using, for example, custom jewel bearings—or etched monoilicon in-plane torsion hinges (or “flexures”).
The present invention is not limited to teachings in those earlier documents. Mirror adjustments by galvanometer scanner and other steering systems are also applicable. Among these earlier documents are teachings of a proprietary CatsEye™ object-warning system. Those documents teach advanced and excellent apparatus and methods for imaging from aircraft and many other kinds of mounting arrangements, both vehicular and stationary, and in many useful practical applications encompassing, merely by way of example, commercial-airline flight-control imaging e.g. from fixed towers, astronautical rendezvous, ground-planned defense maneuvers, and vehicle collision avoidance, as well as terrain mapping from space.
More specifically the above-mentioned earlier documents teach such innovations with greater field of regard (“FOR”) and field of view (“FOV”) than in prior approaches, and with much more nimble and sophisticated capability to notice and optically follow a large variety of objects outside the optical system than previously possible. Even the technologies in those coowned documents, however, leave something to be desired in ability to very quickly steer radiation beams while maintaining the beams at a fine degree of collimation and accordingly maintaining the capability to bring the beams to a very sharp focus.
In this connection the ability to prevent degradation due to diffraction is very important. As our earlier documents show, the fundamental limit imposed by diffraction can be mitigated by use of devices (such as mirrors) that have large apertures, and this is the reason for our previous emphasis on relatively “large” mirrors—but in particular, mirrors up to only a centimeter across.
Likewise our earlier work has emphasized operating steering mirrors in such a way as to yield diffraction characteristics controlled by entire-array dimensions rather than individual-mirror dimensions. These latter techniques do not change the fundamental relationships that govern the diffraction limit (i.e., larger apertures still lead to finer collimation and focus). Rather these techniques modify the functioning of a mirror array to exploit those fundamental relationships much more easily—by increasing dimensions of the array rather than an individual mirror.
Our earlier developments, however, have not fully used the available performance advantages of large mirrors and multimirror arrays.
Neither earlier MEMS devices nor other steering-mirror concepts provide the adequately increased aperture that is needed for best diffraction control. Analogously, earlier relatively large-aperture MEMS devices cannot provide translational stability in the X, Y, and Z axes. Another major inadequacy in prior-art steering deflectors has turned out to be vulnerability to vibration—particularly in high-vibration environments. Two still-further difficulties have been the relatively high power drain required to drive the deflectors, and relatively high mass, weight and bulk of prior gimbal systems. Especially important, in addition to aperture size, is the relatively narrow angular range (field of regard, “FOR”) of prior steering devices.
Certain patent documents have been adduced that at first sight may seem relevant in this field. They include European patent documents and one Japanese patent abstract of two Japanese inventors:                Masayoshi Esashi, with Nippon Signal in Tokyo—particularly in European Patent Application O 686 863 AI at PDF pages 33 and 34 (FIGS. 14 and 15); and        Norihiro Asada, with Nihon Shingo Kabushiki Kaisha—notably in European Patent Application EP 0 774 681 A1 at PDF pages 10, 17 and 39 (FIGS. 1, 9 and 32)—and Asada's EP 0 778 657 A1, at PDF pages 7 through 9 (FIGS. 1 through 4); and Japanese publication 08-166289 of Jun. 25, 1996 in Patent Abstracts of Japan, Application number 06-310657 of The Nippon Signal Company Ltd.        
At least preliminarily it appears that these Japanese inventors have pulled the rug out from under certain of the Draper patents. It is unclear whether any of the Draper claims survives these earlier Japanese inventions. Four other patents of potential interest are U.S. Pat. Nos. 3,742,238, and 4,658,140 (“Infrared scanner for forward loading infrared device”), U.S. Pat. No. 4,470,562 (“Polaris Guidance System”) and U.S. Pat. No. 5,270,792 (“Dynamic Lateral shearing interferometer”).
Conclusion
As noted above, the present state of the art in imaging, while admirable, leaves considerable refinement to be desired.